Hot Deformation Characteristics Of Particles Reinforced 8009 Aluminum Matrix Composites

The 8009 aluminum alloy,a heat resistant Al-Fe-V-Si alloy,exhibits excellent properties such as high strength and thermal stability,due to the presence of high volume fractions of very fine Al₁₂?Fe,V?₃Si nanophase dispersoids.Particle reinforced8009 aluminum matrix composites may further improve the alloy's properties and make the alloy have high elastic modulus,low thermal expansion and high wear resistance,thus they can be good candidates of automotive engine cylinder liners,cylinder heads,pistons and other components to meet the requirements of automotive lightweight,energy saving,environmental pollution reduction and lower production costs.However,due to the great difference between the thermal expansion coefficient of the reinforced particles and the aluminum alloy matrix,the high stress within the composites can be easily formed,which will make the plastic processing performance of the composites far inferior to that of aluminum alloy matrix.Therefore,the hot deformation behavior of particle reinforced 8009 aluminum matrix composites was studied,which could provide theoretical support and technical guidance for the development of a reasonable thermal processing process,furthermore broaden the application range of heat-resistant aluminum matrix composites.In this paper,the 8009 aluminum matrix composites with 15vol.%SiC or Al₂O₃reinforcements?SiC_p/8009Al and Al₂O₃/8009Al composites?prepared by powder direct hot extrusion method were studied,and their high-temperature hot compression experiments were carried out at temperatures of 400-550?and strain rates of0.001-1s^-1.Through the analysis of flow stress,a constitutive model and processing map were established,and the hot compression deformation behaviors of these two particles reinforced 8009 aluminum matrix composites were systematically studied and compared by using microstructure characterization techniques,i.e.XRD,SEM and TEM.Simultaneously,isothermal tensile test and SEM analysis of tensile fracture were performed at below 350?and strain rates of 0.001-0.1s^-1 to study the room temperature and high temperature tensile deformation behaviors of the two aluminum matrix composites.The main results can be summarized as follows:?1?Flow behaviors of SiC_p/8009Al and Al₂O₃/8009Al composites prepared by powder direct hot extrusion method during hot compression deformation were investigated.The hyperbolic sine constitutive equations with Zener-Hollomon parameter Z value and the hot deformation activation energy were established.The flow stresses of SiC_p/8009Al and Al₂O₃/8009Al composites increased sharply with increasing strain and then stabilized at a constant value after reaching a peak value.Both flow stress and stress peak decreased with increasing deformation temperature and decreasing strain rate.The flow stress constitutive analysis showed:The flow stress during hot compression deformation of SiC_p/8009Al composites could be represented by a Zener-Hollomon parameter in the hyperbolic-sine equation that integrates strain,temperature and strain rate,and its deformation activation energy was calculated to be 481-495kJ/mol.Meanwhile,for the Al₂O₃/8009Al composites under hot compressive deformation,the relationship among the peak stress,strain rate and temperature could also be described by the Zener-Hollomon parameter of the hyperbolic sine relation,and its average deformation activation energy was 502.19kJ/mol.?2?Based on the dynamic material model,the processing maps of the SiC_p/8009Al and Al₂O₃/8009Al composites under hot compressive deformation were established.After taking into account the processing map,efficiency of power dissipation and microstructural observations,the optimum processing domains corresponding to 500-550?/0.001-0.02s^-1 for the SiC_p/8009Al composites and530-550?/0.001-0.01s^-1 for the Al₂O₃/8009Al composites were determined.?3?The deformation temperature and strain rate,that is,the effect of Z value on the hot compression deformation of SiC_p/8009Al and Al₂O₃/8009Al composites,and the dynamic softening mechanism during the hot deformation process were revealed.The hot compressive deformation behaviors of SiC_p/8009Al and Al₂O₃/8009Al composites were attributed to intense dynamic recovery resulting from the high volume fraction of Al₁₂?Fe,V?₃Si nanophase dispersoids in the Al alloy matrix.Meanwhile,the accommodation ability between the reinforced particles and the alloy matrix was inhibited by the dispersoid phase,thus the accommodation ability became worse as the Z value increased.Based on the analysis of the hot compressive deformation behavior,the interaction mechanism of dislocations,reinforced particles,dispersed Al₁₂?Fe,V?₃Si phase and matrix during the hot compressive deformation of SiC_p/8009Al and Al₂O₃/8009Al composites were investigated.?4?The tensile deformation behaviors of SiC_p/8009Al and Al₂O₃/8009Al composites at room and elevated temperatures were investigated.The ultimate tensile strength,yield strength,and fracture elongation of SiC_p/8009Al composites at room temperature were 419.8MPa,355.5MPa,and 7.6%,respectively,while those of Al₂O₃/8009Al composites were 326.7MPa,300.1MPa,and 4.8%,respectively.The ultimate tensile strengths and yield strengths of SiC_p/8009Al and Al₂O₃/8009Al composites at high temperature tension decreased with increasing temperature and decreasing strain rate.The fracture elongation slightly decreased at first and then increased with increasing temperature,except at a strain rate of 0.1s^-1 for the Al₂O₃/8009Al composites.The maximum fracture elongation of SiC_p/8009Al and Al₂O₃/8009Al composites at high temperature tension were 9.9%and 5.1%respectively,and its minimum fracture elongation were 4.2%and 3%respectively.The work hardening rates of the studied composites at high temperature tension sharply increased to maxima and then decreased rapidly as the strain increased.Meanwhile,the ultimate tensile strength,yield strength,fracture elongation,and work hardening rate of the SiC_p/8009Al composites were superior to those of the Al₂O₃/8009Al composites under the same conditions.?5?The tensile fracture behaviors of SiC_p/8009Al and Al₂O₃/8009Al composites at room and elevated temperatures were investigated.Compared to 8009Al alloys reinforced with spherical Al₂O₃ particle,8009Al alloys reinforced with irregular SiC particles exhibited a better strengthening effect.The fracture mechanism of the SiC_p/8009Al composites at high temperature tension was mainly ductile fracturing according to the microporous gathering model in alloy matrix,while complemented by the fractures and a small amount of extraction of SiC reinforced particles.The debonding strength between the Al₂O₃ reinforced particles and the Al alloy matrix was weaker,thus it was showed that debonding was primarily fracture mechanism during high temperature tensile deformation for Al₂O₃/8009Al composites,and accompanied by a very small amount of ductile fracture.